The present invention relates to tools for forming features in the joints of structural steel decking and roofing commonly used in large commercial construction, for example, as subflooring for poured concrete floors or as roofing for large industrial buildings. Structural steel decking is typically manufactured in thicknesses ranging from 22 gauge to 16 gauge or more. The decking generally is supplied to the building site in panels ranging in size from 3 feet by 15 feet to about 3 feet by 35 feet. Longitudinal ribs, typically hat sections or flat-bottomed vee sections of from 11/2 to 3 inches in depth are formed in the panels to increase the section modulus of the panels. The individual panels are typically provided with one edge having an exposed upward "male" lip. The opposite edge is provided with a female inverted "U" shaped lip. The individual panels are joined together by placing the female lip over the male lip and crimping the seam at periodic intervals. In many applications, the joints must secure the panels together so as not only to prevent one panel from lifting off the other, but also to prevent the panels from shifting laterally along the seam (along the y-axis as shown in FIG. 1). By holding the panels securely enough to prevent lateral shifting, the assembled decking adds considerable membrane strength to the finished building. Given the inherent weakness of crimped joints to lateral shifting, typically where high membrane strength is required, welding or screwing of the seam is necessary to meet the specified shear strength.
A prior art method for crimping steel decking comprises use of a hand-operated tool shown in FIG. 1, known as the 601 SEAM LOCKER, distributed by Miramar Specialties of Ventura, Calif. The prior art apparatus comprises a compound-lever press in which the operator moves the handles apart to provide the force to crimp the panels together. An optional button punch is provided to upset a portion of the seam to provide some lateral stiffness. Since the apparatus comprises merely a compound lever arrangement, however, it provides a linear multiplication of the force exerted by the operator on the handles. As can be appreciated from the foregoing, hand crimping of thousands of seams is a laborious task and, given the inevitability of operator fatigue, an inherently unreliable method for providing seams having the uniformity necessary to achieve a high degree of lateral stiffness.
Various portable power tools have been developed for setting rivets, crimping sheet metal trusses, and for other applications. For example, U.S. Pat. No. 1,743,209 to Groehn discloses a fastener setting device comprising a toggle-actuated jaw and anvil adapted for setting rivets, particularly in the construction of automobile bodies. U.S. Pat. No. 3,877,280 to Cornell discloses a hand operated power assisted punch and die for crimping sheet metal studs and joists together to form a modular wall panel. U.S. Pat. No. 4,989,438 to Simon discloses a hand-operated power assisted punch and crimp for attaching comer bead to exterior comers in sheet rock or gypsum board walls.
Applicant's prior application Ser. No. 961,162, now U.S. Pat. No. 5,878,617 (incorporated herein by reference) disclosed a pneumatically operated decking crimper having multiple button punches arranged in a staggered configuration. The alternating offset upset portions of the flange formed by the multiple button punches substantially increased the lateral resistance of the crimped seam. However, the inclined walls of the upset portions will tend to pry the seam apart if sufficient side loading is applied. Accordingly, the lateral resistance of the seam thus formed may not be sufficient for some extremely high stress applications. Accordingly, what is needed is an apparatus for producing a crimped joint that has lateral resistance approaching the sheer strength of the roofing panel itself